Process and apparatus for obtaining ink dispersions by subjecting the liquid inks to an ultrasonic or sonic signal

Abstract

A method and apparatus for and aggregates in a fluid medium. The present invention employs an ultrasonic device to efficiently breakup particle agglomerates by driving the ultrasonic signal over a small range of frequencies around the acoustic slow wave frequency of the saturated agglomerate. At this frequency, the fluid vibrates out of phase with the solid and is forced out through the pore structure in the agglomerate. This relative fluid motion to exert high viscous stresses at the particle-particle contact points which leads to fracture of the agglomerate and the redispersion of the individual particles. The apparatus includes a dispersing vessel containing aggregates of particles in a fluid, a sonic member for applying an ultrasonic signal in said dispersing vessel for separating the aggregates to form dispersed particles.

What is claimed is:  
     
       1. A process which comprises subjecting a liquid developer including agglomerates of a thermoplastic resin, a pigment, and a charge adjuvant dispersed in a liquid to ultrasonic signal, said subjecting step comprises applying a predefined acoustic slow wave frequency based upon the agglomerates-particle sizes in said liquid developer to cause liquid to vibrate out of phase with solid portions of agglomerates and is forced out through the pore structure in the agglomerates to break the agglomerates apart. 
     
     
       2. A process in accordance with  claim 1 , wherein said subjecting step comprises breaking apart of the solids of resins, pigment, and charge adjuvant to subsequent to the use of said ultrasonic signal. 
     
     
       3. A process in accordance with  claim 1 , wherein said subjecting step reduces the solids of resins, pigment and charge adjuvant in size subsequent to the said ultrasonic signal being applied thereon. 
     
     
       4. A process in accordance with  claim 3 , wherein said subjecting step comprises applying the ultrasonic signal for a period of time of from about 0.1 seconds to about several minutes. 
     
     
       5. A process in accordance with  claim 3 , further comprising selecting aggregate particles containing from 10 to about several hundred primary particles, or from 1 micron to 200 microns in average volume diameter prior to said subjecting step. 
     
     
       6. A process in accordance with  claim 3 , wherein the particles in size subsequent to the ultrasonic signal being applied thereon from about 0.01 micron to about 20 microns average volume diameter, comprising the primary unaggregated particle size. 
     
     
       7. A process in accordance with  claim 1 , wherein said applying step includes employing a multiple of said acoustic slow wave frequency. 
     
     
       8. A process in accordance with  claim 1 , wherein is said acoustic slow wave frequency determine by the following equation: 
       
         
             f   c=η{S   v   2 (1−φ) 2 }/(2π B φ 2 ρ f )  
         
       
       Where f c  is the acoustic slow wave frequency, η is the fluid viscosity, S v  is the primary particle surface area per unit volume of the aggregate, φ is the aggregate porosity, ρ f  is the fluid density, and B is a phenomenological constant. 
     
     
       9. The process of  claim 8 , wherein the ultrasonic frequency is about −15% to +15% of f c .